Remove commented out cruft
Remove mostly useless and fragile test
Merge Reader::File into Reader

There's really no need for separating these two. It's unlikely that we'll
implement different reading modes (mmap vs in-memory vs file) in Perl, so
we'll just need to pass flags through to the XS code.
Move reader code to PP.pm
Make MaxMind::DB::Reader a shim that loads PP or XS implementation
Fix all tests to work with renamed packages
Make sure all tests run with pure Perl code